In order to authenticate a person's identity, face authentication processes for obtaining a face image of a person and comparing the face image with a previously registered face image of a registrant have been being developed. In the case where images are compared for authentication, it is problematic that the facial features may be altered due to the influence of oblique lighting or illumination effects such as the shade of a tree when the face image of a person is obtained, and therefore the authentication may not be accurately performed.
Japanese Unexamined Patent Publication No. 2007-140723 discloses a technique of calculating a lighting angle of an input image, selecting a filter based on the calculated angle, and defining the facial features of a person extracted from the input image, using the selected filter. This publication discloses that a Gabor filter is used for extracting features, as a Gabor filter is selected in consideration of the size and direction of a lighting angle of each block. Japanese Unexamined Patent Publication No. H11-306348 discloses a technique of designating, when detecting a subject of recognition target such as face, local comparison regions such as eye, nose, lip with respect to an input image in order, normalizing brightness of the designated local comparison regions, and then partially obtaining determination factors with respect to the local comparison regions. Thereby, it is said that a subject of recognition target may be detected without being seriously influenced by the change of environments such as a light source.
Japanese Unexamined Patent Publication No. 2008-9745 discloses a face detection technique using an edge detection filter to detect a face from an image from which the influence of an illumination light is removed.
Japanese Unexamined Patent Publication No. 2009-151539 discloses a technique of determining whether each image of face detection target has a shadow or not and removing the shadow from a cut image which is determined as having a shadow.